core: add wget and ca-certificates
unmount: Remove ' (deleted)' from /proc/mount entries.

Try removing it, or not, in case somebody wants a mount point ending in ' (deleted)'.
Do not run upgrade test if some of the releases are not being tested.
Test: Change /dev/urandom handling
 - Set CROUTON_WEAK_RANDOM in test/run.sh

If CROUTON_WEAK_RANDOM is set:
 - mount-chroot: Select urandom to generate encryption key.
 - Bind mount /dev/urandom to /dev/random in the chroot.
Merge pull request #536 from drinkcat/misc

Add wget/ca-certificates, change /dev/urandom handling + 2 minor fixes.